1. Field of the Invention:
The present invention relates to a process for preparing a smoke-retardant polyisocyanurate foam which simultaneously has properties of low smoke-generation, low friability, not bursting (ie., not scattering as a powder when touched to a flame), and excellent heat-resistance and flame-resistance.
2. Description of the Prior Arts:
Polyisocyanurate foams have been prepared by blending and stirring an organic polyisocyanate, an isocyanate-trimerization catalyst and a blowing agent and if necessary, a surfactant, (Japanese Patent Publication Nos. 33910/1970 and 2269/1971). Such polyisocyanurate foams have excellent heat-resistance and flame-resistance but suffer from the disadvantages of friability, bursting when touched to a flame and smoke-generation when initially touched to a flame.
In order to improve these disadvantages, various processes for preparing modified polyisocyanurate foams have been proposed, for example a method of using a polyether as a modifier (Japanese Patent Publication Nos. 42386/1971 and 2269/1971); a method of using a polyester as a modifier (Japanese Patent Publication No. 28919/1972); a method introducing a polyoxazolidone linkage (Japanese Patent Publication No. 32800/1974); a method of using a polyether polyol having a molecular weight of higher than 200 and a diol having a molecular weight of lower than 200 as a modifier (Japanese Unexamined Patent Publication No. 101497/1973); a method of using a precondensate of xylene resin (Japanese Patent Publication No. 32757/1972); a method of introducing polycarbodiimide linkage (Japanese Patent Publication No. 4591/1971); a method of introducing a urethane linkage and carbodiimide linkage (Japanese Unexamined Patent Publication No. 30796/1972). These modified polyisocyanurate foams have improved friability and bursting property which are imparted by the modification, but still have the disadvantages of decreased flame-resistance and flame-retardance and high smoke-generation. No process for preparing a polyisocyanurate foam which simultaneously possesses the four characteristics of low-smoke-generation, low friability, high flame-resistance and high flame-retardance has yet been proposed.
The inventors have sought to obtain a process for preparing a polyisocyanurate foam having said four characteristics.